Digital data such as audio data recorded in a rapidly accessible storage medium such as a CD (compact disc) can be copied rapidly and easily, and such copied data is almost equivalent in quality to the original data. Thus, it has been strongly demanded to take effective measures against illegal copying in order to protect the copyright of digital data, and various techniques against illegal copying have ever been proposed.
To protect the copyrights of audio content and video content, there have been proposed digital watermarking techniques by which copyright management information used for copying control, playing control, tracing history of copying or the like is embedded into main data such as audio data or video data in a form which will not influence the main data.
As a typical example of such digital watermarking techniques, SDMI (Secure Digital Music Initiative) is well known. For example, in case digital watermark information is embedded in audio data by the SDMI technique and the audio data is reproduced by a player supporting the SDMI technique, the player has to detect the digital watermark information for selection of an audio content (including also recording control and playing control).
For example, a data recording apparatus having an interface complying with the 1394 serial bus standard of the IEEE (Institute of Electrical and Electronics Engineers, Inc.) (will be referred to as “IEEE 1394 interface” hereunder) is constructed as shown in FIG. 1. It should be noted that in this case, the digital watermark information is embedded in audio PCM data.
As shown in FIG. 1, the data recording apparatus is supplied at an input terminal 1 thereof with compressed audio data from a data playing apparatus having the IEEE 1394 interface. In the data playing apparatus, the compressed audio data is subjected to output-limiting as shown in FIG. 2 before outputting to the data recording apparatus. That is, the compressed audio data is outputted from the data playing apparatus via the IEEE 1394 interface to the data recording apparatus. For outputting the compressed audio data, for example SCMS (serial copy management system) information is used to limit the outputting via the IEEE 1394 interface, which will be described in detail below with reference to FIG. 2.
First in step S1, a system controller 10 included in the data recording apparatus communicates with an output destination via an IEEE 1394 interface 2 also included in the data recording apparatus and judges whether the output destination supports the IEEE 1394 interface 2 (will be referred to as “compliant device” hereunder). When the result of judgment is that the output destination is not any compliant device, the system controller 10 goes to step S5 where the compressed audio data will be encrypted for outputting with an encrypt key for decryption of the encrypted data not sent to the output destination. Thus, the noncompliant device is inhibited from decrypting the encrypted data. It should be noted that in step S5, neither the encrypted data nor the encrypt key is passed to the output destination which is not any compliant device, as another way of disabling the device from decrypting the encrypted data.
When it is judged in step S1 that the output destination is a compliant device, the system controller 10 goes to step S2 where it will judge whether the output destination as a compliant device is a recorder or not. When the output destination is no any recorder, the system controller 10 jumps to step S4 where the compressed audio data will be encrypted for outputting and the encrypt key for decryption of the encrypted audio data will also be sent to the output destination.
When it is judged in step S2 that the output destination is a compliant device, the system controller 10 goes to step S3 where it will interpret the SCMS information to judge whether the information means “copy allowed for one generation”. When the result of interpretation of the SCMS information is that the recording is inhibited, the system controller 10 goes to step S5 where the compressed audio data will be encrypted for outputting but the encrypt key for decryption of the encrypted data will not be sent to the output destination.
When the result of interpretation of the SCMS information in step S3 is that the recording is allowed, the system controller 10 goes to step S4 where the compressed audio data will be encrypted for outputting and the encrypt key for decryption of the encrypted data will also be sent to the output destination. That is, the compressed audio data will be transferred to the compliant recorder via the IEEE 1394 interface 2.
As above, since the outputting via the IEEE 1394 interface 2 is limited, the data recording apparatus being the data-transfer destination is enabled to decrypt and record the encrypted data only when the SCMS information means that copying is allowed, but the data recording apparatus cannot decrypt the compressed audio data and record the data normally when the SCMS information means that the recording is inhibited.
Data processed and sent as above is supplied to the data recording apparatus in FIG. 1 via the input terminal 1 and to a decryption circuit 3 via the IEEE 1394 interface 2. When the recording is allowed, the encrypt key is also sent along with the encrypted data. The data recording apparatus acquires the encrypt key via the IEEE 1394 interface 2 and causes the decryption circuit 3 to decrypt the encrypted data with the encrypt key.
The compressed audio data decrypted in the decryption circuit 3 is supplied to a decompression circuit 4 in order to detect digital watermark information (indicated with a reference “WM” in the illustration) embedded in audio PCM (pulse code modulated) data, and the compressed data is decompressed or expanded for decoding. The expansion-decoded audio data is supplied to a recording control circuit 5.
Audio PCM data from the decompression circuit 4 is also supplied to a digital watermark information detection circuit 6 which will extract copyright-protective additional data having been embedded in the audio PCM data by the digital watermarking. Similar to the SCMS information, the additional data indicates “one copy allowed”, “copy inhibited”, “copy-free” or the like, for example.
The system controller 10 includes a microcomputer for example, and interprets digital watermark information from the digital watermark information detection circuit 6. When the digital watermark information means that copy is inhibited, the system controller 10 controls the recording control circuit 5 to inhibit the recording. That is, the system controller 10 inhibits the audio PCM data from being supplied to the circuits downstream of the recording control circuit 5, for example.
When the digital watermark information is interpreted to is “one copy allowed” or “copy-free”, the system controller 10 allows the recording by controlling the recording control circuit 5 to supply the audio PCM data to the downstream circuits. The audio data from the recording control circuit 5 is supplied to a digital watermark information rewrite circuit 7. Then, when the digital watermark information is interpreted to be “one copy allowed”, the system controller 10 controls the digital watermark information rewrite circuit 7 to rewrite the digital watermark information from “one copy allowed” to “copy inhibited”.
The audio PCM data from the digital watermark information rewrite circuit 7 is supplied to a compression circuit 8 where it will be compressed again and supplied to an encryption circuit 9 where it will be encrypted. Further, the encrypted data from the encryption circuit 9 is supplied to a recording modulation circuit 11 where it will be subject to predetermined modulation for modulation (will be referred to as “recording modulation” hereunder). Then, the output from the recording modulation circuit 11 is supplied to a write head 12 which will record the data to a recordable optical disc 13. The optical disc 13 is rotated by a spindle motor 14 driven at a predetermined velocity under the control of a servo circuit 15. It should be noted that the system controller 10 has connected thereto a key-control unit 16 having keys which are operated by the user for entry of a command and data, and an LCD (liquid crystal display) unit 17 as a display element to provide the user with necessary display information.
As above, in the data recording apparatus illustrated in FIG. 1, audio data can securely be transmitted via the IEEE 1394 interface 2 and the recording is controlled according to digital watermark information to positively protect the copyright of the audio data. It should be noted that it has recently been proposed to digital watermark information to limit the data reproduction in the data playing apparatus.
It should be reminded here that it has so far been proposed to embed digital watermark information in main data by spectrum spreading, embed digital watermark information around a high-energy portion of main data, or embed digital watermark information in main data under the effect of masking. In any of these techniques, however, the detection and rewrite of digital watermark information will cause the recorder and player to be heavily loaded, resulting in a degradation in performance of the apparatuses. In recording of a compressed content whose copyright is securely protected as having been described above with reference to FIGS. 1 and 2, it is necessary to decrypt encrypted data and decompress or expand compressed data to restore PCM data for subjection to detection of digital watermark information. For recording the data, it is necessary to encrypt and compress the data again, which causes the performance of the apparatuses to be degraded. Also, such extra operations will disadvantageously add to the power consumption. Further, it takes more time in many cases to detect digital watermark information, and the time from a user's operation of a recording or playing start key until an actual start of recording or playing is longer, which will cause the user to feel something strange.